The effect of freezing temperature on physiological traits in sunflower

This study was conducted to identify the physiological mechanisms associated with the resistance and tolerance of young sunflower plants to freezing temperatures. The effect of overnight temperature -3°C on the maximal quantum efficiency of PSII (Fv/Fm), the relative electrolyte leakage (REL) and the osmotic potential (Ψπ) was determined in five genotypes of sunflower: C33, C98, C124 and C148 were chosen from the population of recombinant inbred lines (RILs) based on contrasted responses to low temperature, and a wild genotype 2603 that was chosen for its ability to maintain activities in cold conditions. The night temperature -3°C over the course of 10 h caused an immediate significant decrease of Fv/Fm in C33, C98, C124 and C148. In the case of genotype C98, the effect of this freezing temperature was manifested by a significant increase of REL. Significant changes of Ψπ, as a reaction to the effect of freezing temperatures, were not found in any of the monitored genotypes. The measurements of the physiological traits after 5 days of regeneration indicated the renewal of integrity of cellular structures and an increase of PSII reaction centre efficiency in all monitored genotypes. From the point of view of tolerance or sensitivity, the wild genotype 2603 showed itself as tolerant towards the tested freezing temperature, displaying insignificant differences with control plants in all monitored traits. Genotype C98 appears to be the most sensitive from the monitored set, with evident changes in two traits signalling frost damage.